Color FPDs having integral light sources are known as FPD modules. Specifically, there are three general categories of color FPDs: reflective color FPDs, transmissive color FPDs, and transreflective color FPDs.
Reflective color FPDs typically require a front light source or front light pipe in order to be viewed in low-light conditions. Such front light sources, however, typically decrease the overall reflection of the FPD, thus causing the FPD to appear “washed out.” In addition, such light sources add to the overall thickness of the FPD module, again making them non-ideal for use in small electronic devices, such as mobile devices.
Transmissive color FPDs typically require a rear light source, which remains continuously on while the FPD is in use. Transmissive color FPD modules thus consume relatively large amounts of power and add a significant amount of overall thickness to the FPD module. Moreover, transmissive color FPD modules are typically difficult to read in strong ambient lighting conditions, such as sunlight.
Transreflective color FPDs combine the performance of reflective and transmissive displays. They can reflect ambient light as well as transmit light from a rear light source. Transmissive color FPDs similarly require a rear light source. The rear light source in a transreflective color FPD module, however, is typically only turned on in low-light conditions. Nonetheless, the rear light source in a transreflective color FPD module adds to the overall thickness of the FPD module.
It is also known to use an electroluminescent (EL) light source with a monochrome FPD. In comparison to the light sources typically used for color FPDs, an EL light source is thin and inexpensive.
A transreflective FPD module with low light emission characteristics is generally considered difficult to view in low light conditions, but is generally acceptable with moderate ambient lighting conditions.